In wireless communication systems, such as a 3GPP Wide Band Code Division Multiple Access (WCDMA) system (3GPP TS 25.211, “Technical Specification Group Radio Access Network; Physical Channels and Mapping of Transport Channels onto Physical Channels (FDD)”, December 2005) a rake receiver is used to receive signals transmitted over a wireless channel. A rake receiver typically performs maximum ratio combining of the received signal by combining the received signals of different paths on the channel proportionally to the strength of each path. The rake receiver assumes that the channel has a limited number of paths and assigns a rake finger to each of the paths. Each rake finger implements the operation of descrambling and/or despreading the received signal where the timing at which the sequence of the signal is taken corresponds to the channel path delay to which the rake finger is assigned. The signal output from the rake receiver can be passed to a decoder for decoding the signal.
The signal is typically sampled at a sampling rate 1/T, where T is the time spacing between samples. The sampling rate is generally chosen to be small in order to save power and memory usage in the receiver. However, according to the Nyquist theorem, the signal should be sampled at a sampling rate which is at least two times the bandwidth of the signal in order for recovery of all of the data in the signal to be possible. This means that a signal is typically sampled at a rate of approximately two times the bandwidth of the signal. The sampled signal is typically passed to an interpolation filter which samples the signal with a sampling rate of
            N      I        T    ,where NI is an oversampling factor used by the interpolation filter.
With reference to FIG. 1a there is shown the timing of the signal samples which are input to the interpolation filter 106 having a time spacing between the samples of T. The timing of the samples taken by the interpolation filter is generally not perfectly aligned with the timing of the incoming signals. FIG. 1b shows the timing of the samples which are output from the interpolation filter having a time spacing between the samples of
      T          N      I        .The interpolation filter can only correct for timing errors of more than
  ±            T              2        ⁢                  N          I                      .  This means that, due to the finite sampling rate of the interpolation filter, timing errors of less than
  ±      T          2      ⁢              N        I            are not corrected by the interpolation filter.
Increasing the oversampling factor of the interpolation filter allows the interpolation filter to correct smaller timing errors. Therefore the precision at which the path delays can be matched improves as the oversampling factor is increased. The value of the path delay can be matched by the interpolation filter with a precision of
      ±          T              2        ⁢                  N          I                      ,as would be apparent to one skilled in the art. It is therefore advantageous in terms of correcting for smaller timing errors to increase the oversampling factor used in the interpolation filter. However, increasing the oversampling factor used in the interpolation filter increases the complexity of the system. Increasing the complexity of the system can be problematic in that the performance of the system can be adversely affected.